Light sources are widely used as signaling devices. Common examples are the brake or turning lights of vehicles, running lights on boats, snowmobiles or aircraft, the emergency lights of police vehicles and ambulances, and lights used on school buses to signal caution or require stopping. In all such uses, it is important that the light source have high visibility, such that even a driver or other person who is not directly attending to the vehicle or other object that is signaling will take note of the signal and fully recognize its significance. On the other hand, a light source used as a signal should not be so attention-getting that it is overly distracting or that it in any way impairs the vision of those that see it.
The most common light signaling sources used on vehicles are incandescent lights. Color and brightness are used to enhance visibility and to indicate certain kinds of signaling. Many light sources used for signaling emit no light until a signal is necessary. Some are simply turned on when the signal is desired and turned off when it is no longer desired. Others are turned on and off with a given frequency or reflected in a varying pattern. Still others change from a base level of light intensity to a somewhat higher intensity as the message to be signaled changes.
For several years ambulances and police vehicles have sometimes used flashing, high intensity, stroboscopic type lights to command attention. Similar high intensity lights are also used on aircraft or on high buildings. These can be quite effective, but their brightness at close range can be so intense that it distracts or is uncomfortable to observe. Accordingly, there is a need for a light source that can be used for signaling and that is both attention-getting and not unduly distruptive or uncomfortable for observers.